The object of the invention is the development of a process for the production of 5-arylidene hydantoins substituted or unsubstituted in the aromatic nucleus by condensation of the corresponding substituted or unsubstituted aromatic aldehyde with hydantoin in the presence of a carboxylic acid.
5-arylidene hydantoins are important intermediate products for the production of phenylalanine and phenylalanines substituted in the aromatic nucleus.
It is already known to produce 5-arylidene hydantoins by condensation of benzaldehyde or substituted aromatic aldehydes with hydantoin in the presence of acetic acid and anhydrous sodium acetate (Wheeler and Hoffmann, Amer. Chem. J. Volume 45, pages 368-383 (1911)). In the reaction of benzaldehyde, the yields, for example, are 70 to 80% based on the hydantoin employed. However, to produce these yields, there is required the use of relatively large amounts of anhydrous sodium.